1. Field of the Invention
The present invention relates to a fluid dynamic bearing device rotatably supporting a shaft member by a dynamic pressure action in a non-contact support through the intermediation of a fluid (lubricating fluid) generated in a radial bearing gap. This bearing device is suitable for use in a spindle motor of an information apparatus, for example, a magnetic disc apparatus, such as an HDD or an FDD, an optical disc apparatus, such as a CD-ROM, a CD-R/RW, or a DVD-ROM/RAM, or a magneto-optical disc apparatus, such as an MD or an MO, the polygon scanner motor of a laser beam printer (LBP), or the small motor of an electric apparatus, such as an axial flow fan.
2. Description of the Related Art
Apart from high rotational accuracy, an improvement in speed, a reduction in cost, a reduction in noise, etc. are required of the motors as mentioned above. One of the factors determining such requisite performances is the bearing supporting the spindle of the motor. Recently, as such the bearing, use of a fluid dynamic bearing superior in the above requisite performances is being considered, or such a fluid bearing has been actually put into practical use.
For example, in a fluid dynamic bearing device to be incorporated into the spindle motor of a disk apparatus, such as an HDD, there is used a dynamic pressure bearing that is equipped with a radial bearing portion supporting a rotary member, which has a shaft portion and a flange portion, in the radial direction in a non-contact support, and a thrust bearing portion supporting the rotary member in the thrust direction in a non-contact support (see, for example, JP2002-61641A). In the dynamic pressure bearing, dynamic pressure grooves as dynamic pressure generating means are provided in the inner peripheral surface of a bearing sleeve constituting the radial bearing portion or in the outer peripheral surface of the shaft portion opposed thereto. Further, dynamic pressure grooves are provided in both end surfaces of the flange portion constituting the thrust bearing portions or in surfaces opposed thereto (e.g., an end surface of the bearing sleeve, or an end surface at the bottom of a housing).
As information apparatuses are improved in terms of performance, efforts are being made, regarding fluid dynamic bearing devices of this type, to enhance the machining precision and assembly precision of their components in order to secure the high bearing performance as required. On the other hand, as a result of the marked reduction in the price of information apparatuses, there is an increasingly strict demand for a reduction in the cost of fluid dynamic bearing devices of this type. Further, today, there is a fierce competition to develop information apparatuses reduced in size and weight, and as a result, there is also a demand for a reduction in the size and weight of fluid dynamic bearing devices of this type.
A housing is equipped with a substantially cylindrical side portion and a bottom portion closing an opening at one end of the side portion. The bottom portion may be formed integrally with the side portion, or separately from the side portion. In the latter case, a fixing portion is previously provided in the inner periphery of one end portion of the side portion, and a member (bottom member) constituting the bottom portion is fixed to this fixing portion by press-fitting, adhesive, etc.
In recent years, an attempt has been made to replace the housing, which has been a machined metal material, with an injection molding formed of a resin material in order to achieve a reduction in the cost and weight of fluid dynamic bearing devices. In particular, in the case of a housing whose bottom portion is formed as a separate bottom member, the realization of a resin housing is often attained by forming exclusively the side portion of a resin molding while forming the bottom member of a metal material, such as brass or an aluminum alloy as in the prior art. When thus forming exclusively the side portion of a resin molding, it is common practice to provide the gate of the injection resin molding at the portion constituting the fixing portion after injection molding. In this case, the fixing portion is formed by machining after cutting the gate.
It should be noted, however, that the dimensional accuracy required of the fixing portion of the side portion is generally strict, and the machining thereof must be conducted meticulously. Thus, an increase in machining cost is unavoidable, which means the advantage in terms of cost attained by using resin cannot be enjoyed to a sufficient degree. Further, there is a possibility of foreign matter generated as a result of machining remaining at the fixing portion. In that case, such foreign matter may enter the interior of the bearing device after the press-fitting of the bottom member and constitute a contaminant, thereby deteriorating the bearing performance.